There is an actuator which has a function to detect a position of a mover (see Patent Literature 1, for example). The electromagnetic actuator described in Patent Literature 1 is constituted by a coil serving as a magnetomotive force generation source, a yoke serving as a magnetic path, a core serving as the mover, a plug nut that can be engaged to the core, a spring that pushes the core toward a position away from the plug nut, a large magnet and a small magnet that generate magnetic fluxes in the yoke in mutually opposite directions, and a magnetic sensor that detects the direction of the magnetic flux flowing through the yoke.
In an initial state, the core is biased by the spring so as to be held in an initial position away from the plug nut. In this initial state, in the magnetic flux flowing through the yoke in the vicinity of the magnetic sensor, the magnetic flux from the large magnet is dominant, and therefore the magnetic sensor detects the direction of the magnetic flux from the large magnet.
When the core is moved from the initial state by the magnetomotive force of the coil so as to be engaged with the plug nut, the magnetic flux from the large magnet flows through the plug nut and the core while bypassing the yoke in the vicinity of the magnetic sensor. In this state, in the magnetic flux flowing through the yoke in the vicinity of the magnetic sensor, the magnetic flux from the small magnet is dominant, and therefore the magnetic sensor detects the direction of the magnetic flux from the small magnet.
The large magnet and the small magnet are disposed so as to generate magnetic fluxes in mutually opposite directions, and therefore the position of the core relative to the plug nut is recognized by detecting variation in the direction of the magnetic flux flowing through the yoke using the magnetic sensor.